1. Field of the Invention
The present invention relates generally to devices and methods used to detect defects in isolation and insulation in electrical wiring. More specifically, the present invention relates to devices and methods that detect defects in a specialized test gas environment.
2. Description of Related Art
Wires or cables typically have a conductor made from conductive material. Characteristically, conductive material is a class of material incapable of supporting electric stress, such that when a charge is given to a conductive material it spreads to all parts of the material. Exemplary conductive materials include aluminum, copper, platinum, gold, silver, chromium, tungsten, nickel, combinations thereof, and the like.
The conductors of wires are commonly coated with a solid insulating material primarily to provide electrical isolation between wires. In addition to its primary function, the solid insulation material also helps provide thermal insulation, strain relief, protection against mechanical damage and abrasion, chemical and corrosion protection, sealing, and limit signal distortion. The thickness and dielectric characteristics of this solid insulation are specifically chosen to maintain isolation, limit shock danger and signal distortion seen in the conductor. As wire is used for a wide variety of purposes, there are differences in the type of insulation used. For example, a data communication cable may use a Teflon(copyright) FEP coat to promote transmission and provide physical protection.
Occasionally the solid insulation surrounding conductive wires is damaged or defective. The damaged or defective solid insulation may expose the conductors. The damage or defects in the insulation may be very small and difficult to see. Defects, such as cracking, often results from mechanical stresses imposed upon conductors having brittle insulation. Embrittlement of the insulation is a result of the normal aging of the insulation. Aging is often accelerated by cable operation at high temperatures over an extended period of time. Mechanical stresses may be caused by short-circuit currents, thermal expansion and contraction of the conductors, movement of the conductor, and vibration. While the dielectric strength of insulation is not significantly reduced by brittleness alone, loss of isolation can result from the development of cracks. For this reason, close inspection of insulation should be made at frequent intervals, and repairs made as necessary.
More specifically, it is important to know if insulating material surrounding a conductive wire or cable has been pierced or broken. Such a defect could be a precursor to an electrical failure in the overall electrical system in which the wire or cable is installed. Similarly, isolated conductors, which are too close together, such as exposed pins in a connector or conductors in an automobile fuse box, may cause an electrical short circuit. Bent or damaged conductors may violate the air gap distances necessary to maintain isolation, thereby introducing a potential short circuit or flashover situation within the electrical system. Failures in the solid wire insulation or uncontrolled short-circuiting between exposed conductors have caused numerous accidents in aircraft and other vehicles. It is therefore desirable to find damaged insulation and verify conductor isolation before a failure occurs so that appropriate repairs can be made.
Unfortunately, the defect and fault detection methods presently available are counterproductive to the defect detection process. For example, high voltage is commonly used to find defects in solid insulation, but the voltage required to find these insulation defects is often higher than the voltage rating of the insulation. Thus the test itself can actually destroy or weaken the insulation and wiring being analyzed, thereby creating defects in the solid insulation. What is needed is a method of reducing the voltage required to detect defects and electrical isolation faults in the electrical pathways.
Furthermore, traditional high voltage testing methods may not be used for wiring located in fuel rich operational environments, such as near jet engines. Applying a high voltage in such an environment creates a substantial risk of combustion unless all of the fuel is removed prior to testing. Some testing methods, such as introducing an ion cloud without displacing the oxygen, actually increase the risk of a spark igniting the fuel.
Accordingly, what is needed is an improved technique for testing insulation and isolation defects in electrical wiring. In particular, the test should not compromise the integrity of the wiring being tested nor be the cause of additional damage to the wiring. Additionally, a method of testing wiring for defects in unstable environments, such as a fuel rich jet engine environment, without generating a substantial risk of combustion is needed.
The present invention provides a system and method of detecting breaches in solid insulation and detecting insufficient air gaps between conductors. The invention performs these detections in a specialized gas environment tailored for high voltage defect sensor applications. The present invention has been developed in response to the current state of the art, and in particular, in response to these and other problems and needs that have not been fully or completely solved by currently available sensor or electronic detection applications. The present invention reduces the amount of high voltage required to detect an insulation or isolation defect when performing a high-voltage breakdown test. These qualities are primarily accomplished through injection of a test gas into the area around the electrical pathway or conductor being tested. Exemplary test gases useful with the present invention include neon, helium, argon, xenon, krypton, radon, and combinations thereof. Helium, for example, has been shown to require a lower voltage gradient than air requires (e.g., at 1500 V and at atmospheric pressure, an arc occurs at approximately 0.009 short-inch in air versus 0.4 inch in helium), and is an excellent choice for the test gas.
The lower voltage gradient of an easily ionized test gas when compared to ambient air helps the system check the solid insulation around wires and cables at a lower voltage potential. The test gas is directed or confined such that it envelops the area to be tested. When high voltage is applied between conductors that are exposed and physically close, a corona forms or an arc occurs between the conductors through the test gas. A testing device may record electrical noise or a current surge between the conductors. Prior to arcing, the added test gas exhibits a very high electrical resistance. Once a sufficient voltage gradient is applied, the test gas xe2x80x9cbreaks downxe2x80x9d or ionizes and has very low effective resistance. With the lower resistance it is easier for an electrical arc to form between the conductors. In an effort to promote this effect at a lower voltage, the voltage gradient for the breakdown of the test gas used in the present invention is substantially lower than for ambient air.
Several configurations are available to test the electrical isolation of the cables in a gas-enriched test environment. One configuration uses a gas-containment shroud to maintain the gas enriched test environment. The gas containment shroud may be flexible and conform to the curvature of the electrical cables. The gas containment shroud may also be transparent, thereby making visible any corona activity around the electrical cables.
A high voltage breakdown tester places sufficient voltage potential across the conductors to detect insufficient isolation or defective insulation. An alternative configuration introduces at least one conductive probe into the shroud environment. The probe is connected to a tester and moved along the conductors. A defect in the insulation is detected when current flow is detected because of an arc between the probe and the conductors being tested. The arc occurs at the location of a defect in the isolation or insulation of a conductor, specifically where the voltage potential between the probe and the exposed conductor overcomes the voltage gradient required for electrical breakdown of the test gas. The application of the test gas by a gas source to a localized region of the conductors enclosed by the gas containment shroud may also be synchronized with a current-sense module on the high voltage breakdown tester to locate an isolation or insulation fault.
Using the characteristics of the test gas, the present invention may also verify the air gaps or required distance between isolated conductors separated by air. Exemplary air gaps include the pins in a connector or exposed conductors in an automobile fuse box. In the present invention, when a pin in a connector is bent, the applied voltage will promote arcing between the closest pins alerting a monitoring test device of the potential short circuit between wires.
Additionally, the system may also be used in fuel rich environments with a substantially lower risk of explosion. As the injected test gas displaces oxygen in the testing area, less oxygen is available for combustion. At certain concentrations of gas there is insufficient oxygen for combustion to occur. The concentration of the test gas in the testing area may be controlled in part by a gas containment shroud, which restricts the movement of the test gas away from the testing area.
The present invention reduces the amount of high voltage required to detect an insulation or isolation defect. The present invention detects the location of insulation defects without damaging the conductor being tested. The present invention allows the safe application of a high-voltage breakdown test for air gaps and insulation defects in fuel rich environments. The present invention enhances the sensitivity of a high-voltage breakdown test with respect to air gaps between conductors in a localized region. As such, the present invention helps verify the required distance between isolated conductors separated by ambient air, such as the pins in a connector or exposed conductors in an automobile fuse box.